Gross on Outlook for String Theory

David Gross just finished giving the closing talk at Strings 2008, on the outlook for string theory, following a talk by Hirosi Ooguri summarizing the conference. Strings 2009 will be in Rome next June, and it appears that there is a tentative plan to have Strings 2010 in College Station, Texas.

Gross began his talk by recalling his days as a postdoc at CERN in the late 60s, working on an early version of string theory (e.g. trying to extend the Veneziano model). At the time he felt CERN was a great center of theory, but somewhat of an experimental backwater, with the real action he was interested in happening at SLAC. Now, forty years later both string theory and CERN have flourished. CERN is in the process of becoming the single world umbrella lab doing particle physics, driving all the others out of business. Unfortunately, Gross sees the same thing happening in particle theory and seems rather pleased about it, saying that only one umbrella in theoretical physics will survive, string theory, eating up everything else. Except LQG, which he says has not yet been brought under the umbrella, and “we’re not sure we want to”.

I found this display of string theory triumphalism truly appalling. The fact of the matter is that string theory has failed miserably to do what it was supposed to do, explain unexplained features of the standard model and predict what happens beyond it. Under the circumstances, to claim victory and write out of particle theory anything that doesn’t fit under the string theory “umbrella” is completely inappropriate. The message to any young particle theorist from Gross was clear: fall in line with string theory ideology, or there will be no place for you under the “umbrella”, i.e. no job for you (the phenomenologists have their own umbrella, you better try that one). The fact that HEP experiment is being forced to consolidate in one lab by economic realities is a really unfortunate one. There is no similar reason for HEP theory to be forced to consolidate around one topic.

Later on in the talk, Gross started channeling Lee Smolin and me, urging young people to stop sticking to the same well-worn ideas, to stop looking under the same lampposts, and to go out and search for something really new. He argued that they would find wandering in the darkness less competitive since few people were doing it. It was unclear whether one is allowed to get out from under the umbrella when one goes out to investigate the darkness, presumably not.

While he made lots of positive comments about current work in string theory in order to rally the troops, much of his talk was rather pessimistic and critical of trends in string theory research. He acknowledged that there hadn’t been any “great breakthroughs” in the field in quite a while. String phenomenology was described an attempt to make string theory “a predictive, or at least imitative” framework. He didn’t comment on what it means for theorists to give up on predicting nature, and settling for imitating it.

About the LHC, he acknowledged that it is unlikely to have anything to say about string theory. He finds the idea of seeing black holes, strings, etc. “extremely unlikely”, but is betting that the Higgs and supersymmetry will show up. Unfortunately, even if supersymmetry is found “it’s not clear that we’re going to learn enough”, this won’t answer any deep questions about string theory or prove that it is relevant. His “most optimistic hope” is that the LHC will see something unexpected, and “we will realize that this was an obvious prediction of string theory”. He notes that this is “almost our last chance”, if nothing relevant to string theory shows up at this energy scale, it is unlikely that anything relevant will show up at any energy scale accessible for an extremely long time.

Gross commented on two topics that hadn’t been mentioned in the talks. He’s still hoping for a non-anthropic explanation of the CC, and noted that no speaker had brought up the anthropic landscape explanation of the CC, with it getting a mention only at one after-dinner talk. Despite what Susskind claims, perhaps the battle between the anthropicists and their opponents is not going so well for the anthopic side. They may get pushed out from underneath the umbrella…

The second topic was the still unsolved question of “what is string theory?”. Gross noted that there were no talks on string field theory, since it and most other ideas about how to define string theory non-perturbatively have gone nowhere. The one thing that is still alive is AdS/CFT, which now completely dominates the subject. More and more, particle theory research under the umbrella is focused only on things related to the duality of N=4 SSYM and string theory on AdS5 x S5. Gross noted the progress toward showing this duality, with the planar limit perhaps being done within the next few years.

By the way, in Ooguri’s talk, he mentions an AdS/CFT discrepancy that has been resolved, saying he was surprised that some blogger didn’t claim this discrepancy as disproof of AdS/CFT. Lubos in his commentary helpfully explains that Ooguri was referring to “numerous pigs and Woits”. Since I’ve never argued that there’s a problem with AdS/CFT duality, I guess he must be talking about someone else. Maybe Jacques Distler has some postings about problems with AdS/CFT that I missed.

Gross takes the attitude that there is no more value in working on “tests” of AdS/CFT, that the conjecture is now well-tested and it is time to move on to try and understand what AdS/CFT is good for, especially what it says about the question of “what string theory is?”. The planar limit is just the classical limit, and he discusses prospects for moving beyond it [and beyond AdS/CFT, to other backgrounds]. On the QFT side, this means deforming the gauge theory by non-renormalizable operators, so it is not clear what to do.

Update: More summary commentary and prizes at Resonaances. Clifford Johnson watched Gross’s talk and summarizes it as follows:

David Gross summed it all up, took stock of where we are, and where we aren’t, and looked forward. A sort of “state of the union” speech if you like. And the state is good. Very good indeed.

55 Responses to Gross on Outlook for String Theory

The planar limit is just the classical limit, and he discusses prospects for moving beyond it. On the QFT side, this means deforming the gauge theory by non-renormalizable operators, so it is not clear what to do.

Going beyond the planar limit just means going to finite Nc on the field theory side (and computing g_s corrections in the dual). Non-renormalizable operators are a separate issue: they let you deform away from asymptotically AdS, with the hope of somehow probing properties of flat-space string theory. I wouldn’t have high hopes for that, but then, Gross is smarter than I am….

Thanks for the clarification, I wasn’t careful enough writing that, should have made it clear that Gross was speculating about moving beyond the AdS/CFT duality, changing the background, not just further tests of AdS/CFT at higher orders in 1/Nc. I’ve edited the post slightly to clarify.

There were really interesting things in the meeting, one of them was covered here by Peter. On Wednesday, it happened really nice talks concerning advances towards the proof of renormizability of supergravity N=8 and some useful nice side effect from this, like more efficient ways to calculate the perturbative terms of the usual QCD.

Hahaha! You find the display of string theory triumphalism appalling? And that it failed miserably in its objectives? What about LQG? Did you watch Carlo Rovelli talk? It was pure comedy, to put it lightly. Even he admitted in one of his slides (one of the first, in fact) that the low energy limit of his theory is pretty much work in progress. What a joke! So, if he and his people can’t derive Einstein equations from their formalism, it is not a theory of quantum gravity. It is not even a theory of gravity (let alone the other interactions, or matter content)! His talk should have ended there! Instead he continues, talking about black holes (solutions of the low-energy limit he can’t derive) and diffeomorphism groups (not the Lorentz group we’re interested in, as Alvarez-Gaume put it in one comment), Immirzi parameters (that must be fixed in different ways to get the different answers he wants to achieve), and many other stand-up comedy pieces.

String theory, on the other hand, has GR as its long-distance limit. No doubts about that! And it’s a consistent quantum theory. Therefore, it is a theory of quantum gravity! Crystal-clear! The “phenomenological” work in progress in string theory is the derivation of the effective model for the remaining interactions, which must contain the Standard Model in the energy range of present accelerators. But that requires the understanding of the stringy vacuum, and that is not for the faint-hearted or amateurs. And, of course, there is no deadline to solve that problem. What does that even mean?!

String theory is indeed the only theory of quantum gravity in existence. And by that I mean a theory that can be explicitly shown to contain Einstein gravity in the large-distance limit, and it is an anomaly-free quantum theory. The possibility of construction of such theory should, as a consequence, contain enough freedom to accommodate all the other interactions, and string theory does just that. It even provides a prescription to calculate particle masses and other physics parameters from the geometric properties of the vacuum, once you find it. It is a hard task, but is not impossible. It is by far more likely than LQG being consistent with low energy physics.

The reason why I defend string theory is that it contains too many beautiful and meaningful results to ignore it as one of the greatest achievements in physics (and mathematics). It gives us so many hints that it is correct that it must be so. Just like Gross’ comment on AdS/CFT. It’s like Riemann’s hypothesis: it’s beautiful, it provides so many outstanding results, and it’s verified up to the first 10^13 zeros. It has to be true! But even if it’s not, I thing that it would be also very interesting (if not more), because you would have to explain why the zeros don’t fall on the critical line only for the 10^500th zero, for example. And even if string theory is proved not to contain our world as a solution (which I doubt), you would still have to explain why not! Because you can already model strings to get toy models for particle phenomenology. They are not the real world, but they are not far removed from it. So, even the absence of a solution containing the Standard Model would simply mean that string theory as we know it would have to be slightly extended instead of completely replaced.

In conclusion, I believe that the answer will arrive, and it will come from string theory. But be patient, because there are no deadlines to fill.

“CERN is in the process of becoming the single world umbrella lab doing particle physics, driving all the others out of business. Gross ses the same thing happening in particle theory and seems rather pleased about it, saying that only one umbrella in theoretical physics will survive, string theory, eating up everything else.”

There is a world of difference between Gross’ claim that string theory contains all the great ideas known in particle physics and gravity, and your claim that string theory is “eating up everything else”. You have managed to turn a scientific point that someone was raising (in this case, Gross), into a sociological statement.

String theory contains gravity or gauge theory or non-commutativity or whatever NOT because it is evil and wants to take over other disciplines. It is just an inherent mathematical feature of string theory. To subtly redefine the problem into a sociological one only helps to misguide your untrained and/or gullible readers.

Arun cites hvtek’s claim that “[string theory] gives us so many hints that it is correct that it must be so”
as a
“pinnacle of anti-scientific thinking.”

I disagree. If you had said hvtek could actually be WRONG, I would have agreed. But being “scientific” is an entirely different thing. Trusting an idea that goes through many of the wickets, and trying to take it to its completion so we can reap the full rewards, is in fact the way theoretical physics SHOULD work. Is it conceivable that the idea is wrong? Of course it is. But that is completely beside the point. Doing science is in fact about taking bets that seem reasonable at the time and dealing with ambiguity. HVTEK was emphasizing that at this point the most reasonable bet is string theory.

Here is the status quo as I see it: string theory has all the features of quantum gravity one would hope for, including solutions to black hole puzzles, singularity resolution, holography, possibility of topology change etc. etc. It contains the broad outlines of realistic particle phenomenology including chiral fermions, generations, gauge groups etc. etc. It brings together almost all (if not all) of the most experimentally successful ideas in theoretical physics including gauge symmetry, Lorentz invariance, etc. etc. Experimentally, it is gradually bringing up connections to some condensed matter systems which are experimentally accessible (with some quantitative, but not very well-understood successes).

Any one of these would have been enough to make an idea interesting. It is inconceivable that string theory will have nothing to do with reality, because it already does. The valid question is whether it is going to be a useful tool in doing particle phenomenology, model-building etc. About that: despite all the nonsense claiming the contrary, progress has been steady, so there is no reason to think that we should give up now. Stabilized vacua are only five years old.

hvtek, maybe Rovellis talk wasn’t the best introduction given the audience, but you obviously have no clue what you are talking about. Yes LQG has some severe problems. No they are not the “problems” you mention. That’s just misinformed blather. E.G: The Immirzi parameter is free in the Holst action, Ashtekar choose a value for mathematical simplicity, later it was found that in QM you have to choose it for consistency with BH entropy. Thus Ashtekars original simplifications could not be used. There are no conflicting scenarios for Immirzi, the original choice was purely for mathematical simplicity before its physical meaning and the way to fix it physically became known.

Since the low energy limit is such a joke to you could you please elucidate me how, given any background independent quantum theory, to even construct observables that would indicate it?

After all it is well known that pure gravity does not have good/unique thermodynamics (what is equilibrium in the absence of a timelike killing vector field?), nor energy scales (Black Holes come in all sizes).

And yes, it is probably fair to say that String theory is the only theory of Quantum Gravity, however at the enormous cost of shitloads of stuff that nobody has ever observed (e.g. 11 dimensions) or that is, even in priunciple, unobservable. Furthermore we have control over the theory only in ways (dual, perturbative) that obscure the conceptual questions that a final formulation must answer one way or another.

Hvtek’s claim that string theory is a theory of quantum gravity is not a precise statement. The precise statement would be that string theory is a perturbative theory of quantum gravity since the arbitrary genus amplitudes are finite (again there is a caveat, since there is no proof for arbitrary genus, but string theorists beleive that it is finite). On the other hand, the nonperturbative string theory is less well-defined mathematically, and results like AdS/CFT
are conjectures, and even if true, it is not clear how it can be used to learn something about quantum gravity phenomena. When compared to Loop Quantum Gravity, one can see that LQG is a nonperturbative formulation, and this is the reason why it is difficult to see what is the flatspace limit (although, the recent work of Rovelli and collaborators has shown that the theory has room to accomodate gravitons, and hence the Einstein equations in the classical limit). Hence the claims that the string theory is the only viable candidate for a quantum gravity theory are not true.

“And yes, it is probably fair to say that String theory is the only theory of Quantum Gravity, however at the enormous cost of shitloads of stuff that nobody has ever observed (e.g. 11 dimensions) or that is, even in priunciple, unobservable.”

This is misleading. String theory can have four dimensions as well.

The better way to say it is that string theory allows many classical solutions, of which one specific choice corresponds to ten dimensions. The ten dimensional theory is special only because it gives rise to the easiest perturtbation theory: the worldsheet CFT is free.

“Furthermore we have control over the theory only in ways (dual, perturbative) that obscure the conceptual questions that a final formulation must answer one way or another.”

I have sympathy with this statement. But it depends a bit on what kind of conceptual questions one has in mind. What seems conceptually important at low energies is not always what is conceptually important at high energies. What is important is that the theory should REDUCE at low energies to the expected principles that we know and love at low energies. But I would say that to rigidly hold on to ideas stemming from a manifold-model of spacetime (such as naive spacetime diff. invariance) all the way to Planck scale, is unwarranted.

ft:”When compared to Loop Quantum Gravity, one can see that LQG is a nonperturbative formulation, and this is the reason why it is difficult to see what is the flatspace limit ”
I think the question was about obtaining Einstein’s equations in the low energy limit of LQG, and not about the flat space limit. The fact is that in the low energy limit ST automatically predicts not only the graviton in the spectrum, but also gives Einstein’s equations from the worlsheet CFT beta functions, without specifying the background metric, and LQG does not even come close to achieving this.

I feel the comments made above and indeed the tone set by Peter’s reportage are not indicative of how stirng theorists think at all. This idea of an ongoing battle just isn’t there. We are open to ideas and indeed Rovelli was invited to speak and everyone I met at strings was glad he did. This persistent itch to create and imagine conspiracies of string theorists excluding people really does verge on the paranoid. We are happy LQG people exist its just we choose something different. Each to their own tastes. I simply would encourage construction rather than criticism. Do your work and let others do theirs instead of moaning about hegemonies.

fh, factual question regarding the Immirzi paramater: is there a choice of the parameter that makes the BH entropy come out right for more than one type of BH? first kind of BH can be regarded as calibration, anything after that is a test…

I don’t think I was at all misrepresenting Gross’s comments. People can listen to them and make up their minds. He was explicitly making an analogy between the dominance of CERN in HEP experiment and string theory in HEP theory. You can try and claim that this dominance of string theory is not a matter of sociology, but just reflects its huge success as a scientific research program. I strongly disagree.

David,

I think I was accurately reporting Gross’s comment on LQG, including its tone. In other venues, Gross has publicly made dismissive comments about the subject. He’s clearly no fan of the subject.

I don’t doubt that many string theorists adopt the attitude you endorse of “each to their own tastes”. But I also think that many, including many quite powerful ones, share what I fear is Gross’s attitude that the hegemony of string theory is justified, that ideas that aren’t somehow related to it are just not that interesting. Lubos reflects this attitude in its pure, uncensored form, but in less extreme form some of this attitude seems to be held by a lot of other people.

I am not an expert in the subject, but this conference seem me very interesting. It’s means that we can obtain analytic solutions of Navier-Stokes equations in a completely different way, by means a new and amazing duality, Isn’t it?. Is this new mathematical tecnique powerful and elegant? If it is true, then turbulent flow could be explained by analytic solutions of Navier-Stokes equations. Can we obtain new insights on turbulence?.

Maybe God could have an answer for Lamb’s second question , i.e. why turbulence?

your comments about these matters are stunning. Science is not about “tastes” (even though the postmodern people who have contaminated 99% of Academia by now clearly think otherwise): science is about finding objectively correct answers to well-defined questions, in this case questions about quantum gravity, and it is essential for the scientific method that hypotheses that have been proved incorrect are abandoned, regardless of people’s “tastes”. In the context of sociology, it is equally important to pick people who are able to look for correct answers and not to pick those who aren’t.

Rovelli’s talk at Strings was a very weird experiment. It brought nothing to the participants because it was addressed to an audience that wants to be manipulated by simple propositions with some buzzwords, audience that doesn’t know what a “path integral” or “Wilson line” means, and the speaker had no idea what the participants (theoretical physicists) are working on now, not even approximately: and he was not interested. The talk covered some basic “motivating concepts” that haven’t changed for 10+ years and that haven’t led to any successful checks in the last decade(s) even though they have led to failed tests. And there is arguably no work in loop quantum gravity that could be useful for more well-informed groups of physicists than those who need to be introduced to the concept of a “path integral”.

Every single question after the talk was from a physicist who has already heard about their framework i.e. learned why it is inconsistent. (Rovelli was not interested in the questions, either: the work in LQG has switched from the search for meaningful and relevant ideas to a P.R. business indefinitely promoting a dead horse, motivated by the proponents’ personal interests.) It is likely that this experiment (an LQG talk at a major string conference) will never repeat itself. There’s no reason for another introduction to LQG at future conferences because the string community has already been “officially exposed” to LQG, and there will also be no reason for more detailed talks because the organizers will now be officially able to see why all the other work is wrong (or at least incomprehensible to all of them) so they will regain the freedom to choose all the speakers according to the merit rather than politically correct desires for “diversity”. From this perspective based on the merit, no LQG researcher could make it to a prestigious global annual conference about high-energy theoretical physics.

Rovelli was the only name of a speaker (in English) that didn’t appear in Hirosi Ooguri’s summary of the talks and LQG was drawn as a disconnected piece from “the” theory studied by the participants. And David Gross indeed said, as this blog correctly reviews, that we’re not sure whether we want to eat this discipline, LQG (like other disciplines in the past). And he did say that string theory was a hegemony in theoretical particle physics because it indeed is one and it is one for extremely good reasons that were revealed during the last 40 years. By looking at objective data, your statement that “everyone” was happy that Rovelli was invited sounds extremely bizarre. Every string theorist whom I consider good has been exposed to the assumptions of the LQG framework years ago, because they try to re-answer some very important questions that every expert in the field should care about, and every one of them knows why the LQG answers are incorrect, because it is not difficult to see.

By this category, I mean people like Susskind, Gross, Polchinski, Seiberg, Witten, Strominger, Vafa, and many others. There exists no genuine “open-mindedness” or “freedom to choose physics according to tastes” because these questions have been answered and the only difference is whether physicists choose to be silent about these facts (none of the people in my list has been quite silent about the inconsistency of LQG, though; I could tell you dozens of details based on private conversations but because it might be sensitive, they won’t appear here). It is very plausible that there exist many students and other junior people who are not getting these points because similar topics about “alternative theories” became a part of political correctness that cannot be taught or talked about freely (because it could insult someone to explain why a class of theories is known to be wrong, right?) and they were not able to analyze these problems independently (so far). So people who don’t really mean anything in physics, such as Urs Schreiber, A.J., or someone like that, can be ambiguous about this question: this includes everyone who thinks that the discussions at this blog are intelligent and relevant for actual physics, rather than being emotional exchanges mostly between cranks who have no clue what they’re talking about. But be sure that the physicists who actually represent the “bones” of the skeleton supporting the “lampposts” of string theory are not ambiguous at all. LQG doesn’t work and there is no known promising & surviving route in this context that would deserve to be studied. That’s also why no new LQG person should be hired at any institution that knows what it is doing.

Also, I think that if you actually think that these LQG things have a significant probability to be correct, or they’re not excluded, then all of your work lacks a basic scientific integrity because your papers seem to be assuming that LQG is incorrect but you never state it. For example, all the comments you have ever made about anomalies should supplemented with a citation of an LQG source where it is argued that anomalies can’t exist because they, and all effects coming from UV divergences, might be removed by the “discrete nature of space” at short distances. In all cases, you should honestly consider both possibilities, that LQG is correct and LQG is wrong. The same thing applies to all sections of your papers where you use a classical solution because you should be studying these things in a background-independent way, if the LQG teaching is correct, and so on and on. If you really think that LQG might be correct, your papers are an example of hiding of the facts in science which would probably be even worse than to misunderstand why LQG is wrong.

In other words, if you have the “tastes” that you expressed and you think that LQG is more than a collection of ideas that can only be promising for 1 minute until one makes any test, ideas that are addressed to journalists rather than experts, research programs where all the hopes have already been proved unsubstantiated, you should really work on it because if it were a promising approach to quantum gravity, as you seem to think, then it would surely be an understudied one. Meanwhile, it would be desirable if you stopped trying to intimidate the physicists who actually know why LQG is not serious physics and create dishonest propaganda about “consensus” about your ludicrous opinions about “diverse tastes”, “happiness” about the useless talk, and “encouragement of construction” at corners of the space of ideas where nothing constructive can be constructed.

It would sad if, as you indicate, young people were so absorbed into work under “particular lampposts” that they would become unable to see the big picture and if they become ambibuous about key conceptual questions thare are not ambiguous. But it would be even worse if physics switched into a hypocritical mode where people think something else than what they write in their papers. For me, your comments about LQG were shocking because they seem flagrantly incompatible with everything I have read in your papers and everything we have ever discussed in person.

Wow Lubos, that’s a long post for someone who “Sorry but I really can’t afford to share readers…” of this blog 😉
If ST is so fantastic, why did you quit physics? you complain about production but yours is zero in the last 2 years…

I may agree with you Rovelli’s talk wasn’t very exciting, but neither is ST these days when it comes to QG.

I agree ST has inspired very beautiful and potentially (yet to be seen) useful stuff whereas LQG hasn’t moved pass a few neat ideas but no clear progress. But as a theory of everything is as useful as LQG so far, let alone talk about phenomenology…That’s the reason why there aren’t many jobs out there for string theorists anyhow. Evolution at work…

I quit the Academia in 2005 when the feminist Nazis effectively took over Harvard, after preventing president Summers to say facts about biology that every person who is not a complete idiot knows – e.g. about cognitive differences between sexes. Because I spent the first 1/2 of my life in a totalitarian society, I know what it means to lose freedom of speech and I would never tolerate anything comparable to repeat in the place where I live. At that time I simply decided not to be extending/replacing the H1 visas which expired in June 2007, so I resigned.

But it is true that even if this thing didn’t happen, I would be tempted to run away because of related things that were happening around physics. I got annoyed by people similar to David Berman who were implicitly helping those self-serving fraudsters and liars similar to Mr Woit and Mr Smolin to get away with their lies and to create an unjustified gloomy atmosophere in the field. At least, David Berman is brave enough to sign, but various anonymous people – a moral waste similar to you – apparently began to influence the course of things as well.

Of course if there are people who can’t touch the ankles of David Gross, they won’t be appreciating how fantastic the progress in string theory has been and it is still remarkable. The Strings 2008 conference was kind of impressive and I am convinced that even the people who can follow 10% of the relevant concepts only know why it is the case. At any rate, I just want to keep the freedom to know and say and why a fantastic theory is fantastic and why rubbish is rubbish, and the growing influence of mediocre, dishonest, and often anonymous people on the Academia was incompatible with my unbreakable standards about the scientific integrity. These things began to influence even things like my organization of seminars (lousy speakers wanted to speak about nonsense for the sake of “diversity” all the time, not respecting that they would have to be invited), teaching, etc. The job simply sucked given the existing conditions.

I agree that pigs, Woits, and Smolins have had a very bad impact on the perception of theoretical physics within the public and the broader scientific community, influence funding as well, which is why they deserve a very tough punishment. But you’re still heavily exaggerating the importance of these two jerks and their gullible followers. Concerning jobs, Xi Yin was just hired at Harvard (after Frederik Denef), Allan Adams was just hired at MIT, Jason Kumar was hired at Hawaii, Dan Kabat was hired at Lehman College, and sorry if I missed other people. Add the new stringy IMP (fundamental physics = string theory) center paid for by the Japanese government. That’s arguably a comparable number to the recent years (many of these jobs were announced really recently) and I am convinced that by the next year, the impact of the anti-theorist hysteria supported by the likes of the owner of this blog will completely fade away and everyone, except for a few anonymous posters at Not Even Wrong, will know that the propaganda by Woit and Smolin was based on lies and the anonymous people supporting Woit on this forum are scum if not Woit himself.

String theory is fantastic and whoever doesn’t see it even though he claims to be interested in theoretical physics is simply not a high-quality thinker and I find it unacceptable for these people to dictate what others can think and say about their work or even what they should work on.

I personally do not think LQG is the right approach to the quantum gravity for the many reasons that are well known to the community so Lubos I will not be replacing my papers with LQG citations.

My point was simply that I thought Peter’s description of a conflict between LQG and strings not to be accurate in terms of how people think. In my quote where I said people were happy that there was a LQG talk. I did not say that the same people agreed with LQG but were simply happy to see a talk that could make manifest the issues involved.

I think this was part of the thinking of the CERN committee. After all one of the critical questions that followed was by Alvarez-Gaume who was surely involved in the decision to invite him.

I suppose, Lubos our disagreement is how as string theorists we should behave to people who disagree with us. Your criticisms of LQG as a theory have been valid but I feel you do us no favours by adopting an aggressive attitude. This is a PR question which you don’t like, but I never made any comments about the validity of LQG physics.

To balance this post let me say how exciting strings 2008 was. For me one of the best in recent years both in terms of the work presented in the talks and in the many discussions behind the scenes where people were being genuinely excited by emerging questions. I came away somewhat inspired…

“My point was simply that I thought Peter’s description of a conflict between LQG and strings not to be accurate in terms of how people think.”

I second this from the other side. Though I have to admit there are exceptions, most people don’t.

On another note, the questions to Rovelli were excellent and cut to some of the core conceptual issues of LQG. It’s not that people ignore these questions, it’s just that because the setup of the theory is so different from familiar QFT, that the questions that are most natural/important from the PoV of QFT end up being the hardest to answer.
And then there are genuinely different opinions in the community, and another speaker would have given different answers to his. There isn’t one theory of LQG after all, or even one complete framework.

Even perturbatively, low-energy string theory is not a theory of quantum gravity. It is a theory of wrong (experimentally excluded) gravity with spin 2 graviton accompanied by an unknown number of massless scalar Brans-Dicke fields (dilaton/moduli). So in the first approximation it is some sort of Brans Dicke theory, not Einstein’s GR.

Yes, I agree that Gross’ talk was at least very strange. He should have encouraged the participants to jump away from a sinking ship instead of living in denial.

Come on Peter, you are slipping up — your “Lubos Motl” ‘bot, cunningly designed to make string theory look bad, is looking less and less realistic. Better iron out the bugs and re-launch! Or, better, write an entirely new program. Better make him a US citizen this time, the current implementation is a bit unfair on the Czechs.

I don’t understand why commenters keep referring to my supposedly inaccurate description of the conflict between LQG and strings. The only mention of LQG in the posting was an accurate quote from Gross about it.

As for the main piece of editorializing I did in this posting, objecting to Gross’s string theory triumphalism, I see that Lubos agrees with my description of what Gross said. And as far as I can tell, David (Berman) share Lubos’s point of view, just thinks that the aggressive way he expresses it is unfortunately counterproductive. I fear that this is an all too common attitude among string theorists.

For lots of people, including myself, the attitude towards LQG is basically curiosity mixed with a heavy dose of skepticism. There are sufficient number of really basic problems and unanswered questions to discourage people from jumping in and participating, but that could change in the future. Also, lots of people are completely oblivious to LQG and its main program, being exposed to the media and /or blogs it is easy to forget what a tiny community that is.

fh, probably not the time or place, but ask me in person next time we meet…let me just say that I’d personally would need to be convinced about the very basics – making connection to known conventional physics (apples falling from trees, harmonic oscillators having quantized spectrum,…), before taking seriously any claim about exotic things like BH entropy and big bang bounces, not to even mention some claims of experimental signatures…in other words I think the framework is too undeveloped to discuss applications at the moment.

Dear Lubos,
I wished you had the same passion for science as you do for criticism. Regardless of Academia, I wonder why did you stop contribuiting to ST? Wherever you are right now I’m sure you can still post in the arxiv don’t you? Stopping research due to a bunch of anonymous posts is a bit pathetic don’t you think? What kind of scientist would do that at the first sight of confrontation? Only the weak I should say… or perhaps you just don’t have anything intelligent to say anymore, in which case I would understand your reactions…

Do you truly believe that calling people ‘a moral waste’ can inspire anything more than a laugh? Lubos, if anything, you are really childish, but entertaining gotta admit 🙂

Regarding jobs, we all know MIT and Harvard are 5 year postdocs with teaching duties, perhaps MIT not as much as Harvard though… The rest probably finally woke up to real physics after all… “oops, the LHC.. we forgot…” 😉

Hmmm. I must agree with Lubos that this statement by Rovelli is very grating:

LQG studies the hypothesis that this problem can be addressed in the context of quantum general relativity plus the standard model.

This so called context really makes no sense at all, since the term quantum GR can only really make sense in a theory of QG, and the latter cannot possibly be an ad hoc mixture of GR/SM. This is a serious criticism of LQG, which its proponents, as far as I can tell, have never addressed even qualitatively.

But now I simply must watch Gross’s talk, because his comments on BI sound insightful….

thank you Daniel, it was interesting to read answers to the very explicit criticisms by Lubos. I hope Rovelli knows that there is no point in insisting, as no logical argument will convince Lubos when he wants to believe something else. Debating seems as useless as rationally arguing with a female about emotionally sensible issues.

“From this perspective based on the merit, no LQG researcher could make it to a prestigious global annual conference about high-energy theoretical physics.”

i guess that is true, but it only was a string conference anyways. 🙂

btw: my favorite quote of this conference is from gubsres finite temperature talk. he was presenting some double-peak experimental signal from RHIC with the words: “the first thing you ask yourself when you see these data is of course how to understand them in terms of black holes”
well, yeah. that about sums it up for me.

Gross is saying that string theory subsumes other ideas and thinks of this feature as one of its strengths. You take this to mean that he wants to actively vanquish other ideas. I have never heard any string theorist, let alone Gross, ever make such a cartoon-villain-like statement.

You are of course welcome to have your opinion about how string theory interacts with other ideas, but the problem is when you attribute a claim that was clearly not made by your opponent.

Even at the level of facts (and not just about the incorrect attribution), I am not sure you have got it right. How many good ideas have been killed off because of the prevalence of string theory? Maybe there are some, but I cannot recall even one at the moment. On the contrary, I know some ideas which I think are not exactly well-motivated, but which still manage to survive in academia despite the machinations of the evil string theorists. I can also list a tremendous number of independent ideas in high energy physics that have been naturally subsumed and strengthened by string theory: gauge theories, Riemannian geometry, supersymmetry, supergravity, Kaluza-Klein theories, noncommutative geometry, and many more.

You should address what I actually write, not make things up to attack. I did not say Gross “wants to actively vanquish other ideas”. I did say that Gross is explicitly making a triumphalist argument: that string theory, like CERN, is all that remains. He feels that it has subsumed other, related ideas that are valuable, and that it is now an “umbrella” covering a range of research.

The problem with this is what happens to ideas that don’t fit under the umbrella? I would characterize Gross’s attitude as not that he wants to vanquish such ideas, but that they are already vanquished. Just like CERN, with the LHC, has no competition at the energy frontier, string theory similarly has no competition. This is explicitly what he said.

The problem with the idea that “string theory has subsumed gauge theory” is that there are many important problems in gauge theory that have nothing to do with gauge-string duality, and these now don’t fit under the string theory “umbrella”. Actually, logically the way things should be is that, with AdS/CFT, gauge theory subsumes string theory, with those parts of string theory unconnected to gauge theory being abandoned.

Don’t you think there’s something funny about going on about how one research program now is the umbrella under which everything must fit, when that program has been spectacularly unsuccessful at accomplishing its goals?

Given the fertility of the field of String Theory, rather than of an umbrella, I would speak of a condom. As to Gross’s encouragement to youngsters, it seems like telling them to f*** around unprotected.

Peter says: “You should address what I actually write, not make things up to attack. I did not say Gross “wants to actively vanquish other ideas”. ”

Dear Peter, of course you did not write those specific words. That was my summary of what you say, for example, here:

“Under the circumstances, to claim victory and write out of particle theory anything that doesn’t fit under the string theory “umbrella” is completely inappropriate. The message to any young particle theorist from Gross was clear: fall in line with string theory ideology, or there will be no place for you under the “umbrella”, i.e. no job for you (the phenomenologists have their own umbrella, you better try that one).”

I see no way to NOT characterize this as a threat of aggressive assimilation (hence the word “vanquish”).

Anyway, since you are at the stage where you say I am making things up and attacking you, perhaps further discussion on this topic is unlikely to lead to any clarification.

A comment that appeared here yesterday purporting to come from Renate Loll has been deleted, along with all responses to it. She assures me it was fraudulent. It was submitted by some moron from a Time Warner Cable connection in New York City. Unfortunately, the LQG vs. string theory debate over quantum gravity seems to attract too little serious scientific discussion, and too much idiotic, unprofessional behavior.

Stringers vs. Loopers is starting to eerily parallel Repubs vs. Demos ! The Stringers have been `in-power’ way too long, and the Loopers have not. The Stringers have peverted physics, and lost sight of its constitution, while the Loopers have deviated from the Minkowskian norm, and embraced the Einsteinian vision as reality.
The Stringers have a Lubosian attack dog, and the Loopers a Rovellian troubador. Both await the CERNian election outcome.
May Popper rule the house and senate forever !
And who-in-the-hell co-scheduled Emergent Gravity and Cosmo the same week ?? How are we supposed to go to both, in Cat States ?